In accordance with U.S. Pat. No. 5,401,457 for PROCESS FOR FORMING A COLOR COATED ARTICLE, By Emery I. Valyi, Patented Mar. 28, 1995, a process is provided for forming a color coated article. In accordance with the '457 patent, a film is placed substantially flat over a mold cavity and deformed by a core mold half and by molten plastic entering through a sprue.
An alternate method consists of thermoforming the film to nest accurately in the mold cavity, with said operation being carried out independently of the mold. The formed film insert is then brought to the mold and placed into the cavity. This procedure is described by Ch. Fridley, Avery Dennison, in Product Finishing, Apr. 19, 1992, and European Patent 0,442,128 to Beyer, and other publications. The Avery procedure entails a forming process of the film that is well known and widely practiced for other uses. It is a low pressure process for shaping the film or sheet, in solid condition, at relatively low temperatures. This holds for all of the several variants of thermoforming, such as vacuum forming, whether the vacuum is to suck the film into the cavity, or onto the core, as well as thermoforming followed by a sizing operation.
The result of this is a product whose dimensional accuracy and shape conformance is not within the range of a high pressure forming process, such as injection molding or compression molding. Consequently, the thermoformed preform, while nesting in the mold cavity or slipped over the core, fails to conform to them fully. Thus, upon injecting or compressing plastic behind the preform, the preform will deform producing localized surface imperfections. These imperfections may be dimensionally insignificant but optically discernible and therefore may provide a product of insufficient quality for an automotive finish, for example. In addition, the cost of a separately made film insert is relatively high, considerable trim scrap is generated, and the handling (transport, destacking, insertion) become expensive.
The procedure of the '457 patent overcomes the above defects; however, it is difficult to control, particularly when molding parts with large surfaces and sharply varying curvature. The difficulties increase when the plastic is pressure molded at high enough temperatures to reduce the film strength substantially, as in the case of conventional injection molding.
In applying either of the above processes to large, panel-like structures, it was found, moreover, that the procedure of injection molding of the '457 patent and Avery Dennison procedure referred to above, is difficult to carry out, requiring extremely costly equipment, and prone to produce imperfections at the interface between the film layer and the injected plastic.
U.S. Pat. No. 6,132,669 to Valyi et al. describes a new and advantageous procedure for efficiently molding plastics and incorporating reinforcement layers into the molded products, as well as describing improved products. Long glass fibers, e.g., 8 to 25 mm in length, have been found to improve the physical properties of injection molded plastics as well as products molded in accordance with the aforementioned U.S. Pat. No. 6,132,669. These are particularly advantageous for the automotive industry. Unfortunately, however, the surface appearance of parts molded with long glass fibers is often degraded.
Injection molding is the prior art method generally employed to mold parts with long glass fibers, that is for example with fibers longer than 8 mm and generally from 8 to 25 mm. The physical properties, notably tensile strength and flexural modulus, for parts molded with long glass fibers are significantly improved over conventional molding using short glass fibers, i.e., fibers less than 8 mm in length. However, the main benefits of using the long glass fibers is not achieved with injection molding because many if not most of the long glass fibers are broken by the shear forces of injection molding and the fact that fiber orientation varies with location in the part. Variable fiber orientation creates molded parts with non-uniform properties, which is disadvantageous. Fibrous additives in general tend to degrade the appearance of the part surface, particularly in class A surfaces. Also, the degree of appearance degradation increases with increasing fiber diameter and length. Fiber “read through” from long fibers is a serious limitation on the use of the advantageous long fibers for appearance of the parts molded with the long fibers. This seriously limits the use of the long fibers.
There is, therefore, a need for and it is an object of the present invention to provide an improved process and molded article which advantageously uses long fibers in molded products with minimum fiber breakage and with minimum to no fiber read through at the surface of the molded product.